LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desirable illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption. Therefore, they are considered a cost-effective lighting solution.
Typical LED tube lamps have a variety of LED elements and driving circuits. The LED elements include LED chip-packaging elements, light diffusion elements, high efficient heat dissipating elements, light reflective boards and light diffusing boards. Heat generated by the LED elements and the driving elements is considerable and mainly dominates the illumination intensity such that the heat dissipation needs to be properly disposed to avoid rapid decrease of the luminance and the lifetime of the LED lamps. Problems including power loss, rapid light decay, and short lifetime due to poor heat dissipation are always the key factors in consideration of improving the performance of the LED illuminating system. It is therefore one of the important issues to solve the heat dissipation problem of the LED products.
Nowadays, most of the LED tube lamps use plastic tubes and metallic elements to dissipate heat from the LEDs. The metallic elements are usually exposed to the outside of the plastic tubes. This design improves heat dissipation but heightens the risk of electric shocks. The metallic elements may be disposed inside the plastic tubes. However, heat trapped inside the plastic tubes may cause the plastic tubes to deform. Deformation of the plastic tubes also occurs even when the elements to dissipate heat from the LEDs are not metallic.
The metallic elements disposed to dissipate heat from the LEDs may be made of aluminum. However, aluminum is too soft to sufficiently support the plastic tubes when the deformation of plastic tubes occurs due to the heat as far as the metallic elements disposed inside the plastic tubes are concerned.
A myriad of designs have been contrived to improve the LED tube lamp. Among them are two Chinese patents purported to shape the light coming from the LED light source, to enhance heatsinking efficiency and to facilitate assembly of the LED tube lamp. The Chinese patent CN201320164967.4 filed Apr. 7, 2013 disclosed an aluminum object for LED tube lamps. The aluminum object includes a heatsinking portion, a platform, a left reflective plate and a right reflective plate. At least one reinforcing rib connects the platform and the heatsinking portion, forming an H-shaped structure in the aluminum object. In an embodiment, a pair of reinforcing ribs connect the platform and the heatsinking portion. The pair of reinforcing ribs, perpendicular to the platform, are spaced apart from each other. A screw hole is formed between the pair of reinforcing ribs for fastening the end cap to the lamp tube. Similarly, another Chinese patent CN201010611712.9 filed Dec. 29, 2010 disclosed a light-shaping and heatsinking device for LED tube lamps. The device comprises a base, which includes a pair of flanges at edges of the base for fastening the base to the lamp tube. The base further includes a reinforcing rib in the middle portion of the base. The cross section of the base defines an arc and a chord sitting squarely in the arc. The base further includes a plurality of radiating fins on the outer surface of the base. A platform is formed along the chord for lodging the LED light strip. A reflective plate connects the edge of the base and the platform for guiding the light up to a desired direction. A screw hole is formed between the reinforcing ribs for fastening the end cap to the lamp tube.
The benefits such design bestows upon us are clearly outweighed by the problems arising from it. The LED tube lamps described above include, in common, an aluminum object shaped to do multiple things at the same time regardless of the rest of the lamp tube: shaping the light otherwise aimless straying; providing a mounting base for other parts of the LED tube lamp and providing a heatsink. The aluminum object in the prior art—which is configured to reflect light, dissipate heat and hold the parts together—would have to be bigger, heavier and cost more to make than an aluminum object which is holistically designed to coordinate with other parts of a lamp tube to perform a greater set of functions even better. Moreover, the reflective plate in the prior art, which is meant to bounce light outwards on one side, happens to block light from the other side. Consequently, the LED tube lamp having such reflective plate leaves an eerie swipe of near darkness behind the lamp. Furthermore, fastening the end cap to the lamp tube with a screw and a hole poses security and structural issues. Accidents such as short circuit and electric shock would be more likely, other things equal, when a screw—which is an electrical conductor—is connecting the end cap and the lamp tube than when a non-conductive fastening means is deployed. Additionally, the aluminum object would be more likely to deform under stress when a screw—which by nature is a destructive fastening means—cuts through the object than when a non-destructive fastening means is deployed.
A fluorescent tube lamp includes a lamp tube having, traditionally, a circular cross section—for good reasons. The lamp tube is filled with a gas containing low-pressure mercury vapor and argon, xenon, neon or krypton. The pressure inside the lamp is around 0.3% of atmospheric pressure. The inner surface of the lamp is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The circular cross section provides the lamp tube with structural strength needed to overcome the weight of air on its surface outside the lamp. Other things equal, when a lamp tube provides a bigger inner surface to which fluorescent chemicals are coated, the lamp shines brighter. Lamp tubes having a circular cross section is a sound option. Also, omnidirectional light makes a circular cross section a perfect solution for a lamp tube. An LED tube lamp, however, operates on an entirely different set of principles. Maximizing coating surface is no longer essential for luminous output. Air pressure on the lamp tube becomes irrelevant. Cylindrical lamp tubes, when used in LED tube lamps, induce potential inconvenience if not loss under unfortunate circumstances. An LED tube lamp, whose light is inherently directional, must be correctly oriented before plugging into a light fixture. Cylindrical lamp tubes, unless otherwise pointed out, gives no visual indication of their correct orientation. Moreover, cylindrical lamp tubes roll off the desk easily. Thus, LED luminaries open up whole new possibilities for designing the shape of a lamp tube.